在multilevel regression model中，

In fact, when the intraclass correlation is zero, the total sample of children can be treated as though it were a simple random sample, not a cluster-randomized sample,……
as the magnitude of the intraclass correlation approaches 1, the effective sample size in any statistical analysis approaches the total number of schools in the sample, rather than the total number of children.
所以，我的疑问是，明明计算的是组间相关系数，为啥要成为组内相关系数？
intraclass/interclass correlation 组间组内？